A typical electronic assembly is circuit board that has electronic components, such as PBGAs and flip chips, attached to it. Each of these electronic components has solder bumps on the bottom that are reflowed to attach the electronic component to contact pads on the circuit board.
Consequently, it is conventional practice to underfill the electronic component with a polymeric material after it is attached to the circuit board. The electronic component is vulnerable to damage due to handling and electrical testing. The bottom of the electronic component must be cleaned of flux residue in order for epoxy underfill to be used.
In the present underfill process a liquid polymeric material is dispensed through a needle to two sides of the attached electronic component and then the needle progresses to another attached electronic component to repeat the same process. Meanwhile the underfill material wicks beneath the electronic component and around the solder bumps. After the material wicks inwardly the desired distance, the liquid polymeric material is dispensed to the remaining two sides of the attached electronic component, finishing the underfill coverage.
After the liquid of underfill material is dispensed, the underfill material is cured at an elevated temperature for a given period of time, for example, approximately 1 hour at 150 degrees Centigrade.
After cure, the electronic assembly can be handled with less concern and the electronic component itself and solder bumps are also less vulnerable to damage. The electronic component is normally thermally engaged to a heat sink by contacting thermal grease or the like applied to the top of the electronic component to dissipate heat resulting from operation of the electronic assembly.
This process has an appreciable yield loss due to underfill accidentally curing on the top of the electronic device which interferes with heat transfer when a heat sink is used.